Periprosthetic osteolysis surrounding joint arthroplasties leads to prosthetic loosening and failure and is one of the major issues facing our aging population. It is known that monocytes located in the periprosthetic membrane surrounding total joint arthroplasties secrete cytokines which stimulate bone resorption and lead to implant failure. In particular, tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) have been implicated in the osteolysis which occurs around loose implants. Despite the magnitude and clinical relevance of this problem, little is known about the basic mechanisms of cytokine release in response to wear debris. The applicant proposes to investigate these basic mechanisms with the rationale that understanding of the principles involved in this process will suggest possible therapeutic approaches. The human monocytic cell line, THP-1, has been partially characterized and preliminary work suggests that this cell line is ideal for the investigation of the effects of particulate debris on monocytes. These cells have very low basal levels of cytokine production, respond to stimulation with titanium with large increases in cytokine production and mRNA levels, and are readily transfected with foreign DNA. In this proposal, the characterization of THP-1 responses to titanium will be completed establishing these cells as the first human cell line for investigation of the mechanism of prosthetic loosening. Promoter constructs for TNF-alpha and IL-6 will be transfected into THP-1 cells to determine the cis-acting regulatory regions and trans-activating factors involved cytokine release by wear debris. Preliminary results have demonstrated that cytokine release in titanium-stimulated monocytes is regulated by pharmacological agents which alter intracellular signaling pathways as well as by cytokines IL-4 and IL-10. The effects of these agents on cytokine release and promoter activity will be determined. Since some of these agents, including the phosphodiesterase inhibitor ciprofloxacin and pentoxifylline have possible clinical significance, the potential of these various agents to inhibit bone resorption will be investigated in 1). a periprosthetic membrane organ cultures; and 2) in in vitro bone resorption models. These studies will potentially lay the groundwork for a more complete understanding of the loosening process, shed light on why some individuals loosen and others do not, and lead to possible therapeutic approaches.